Graphene has attracted intensive world-wide attention because of its fundamental and technological importance.1-8 Single-molecule sensitivity was demonstrated9 in graphene-based sensors by monitoring the Hall resistivity in a magnetic field, and a detection limit of the order of 1 part per billion (p.p.b) was estimated from longitudinal resistivity measurement at zero magnetic field. Such exceptional sensitivity is important for industrial, environmental and military monitoring, and thus has been attracting enormous interests from the research and industry communities.10-42 However, despite the great potential of graphene as next-generation sensing device, there remains a major obstacle for its use in practical applications, which is the mass production of arrays of graphene sensors with a reliable and low cost method. Recently, steady progresses have been made on the production of graphene by the chemical vapor deposition (CVD) approach,43-69 and since 2009 low-cost production of large-area single-layer graphene has been achieved by a CVD process on copper substrate.43 Yet the underlying Cu substrate is heavily conducting, which renders the electronic contribution from graphene negligible. As a result, one usually adopts complicated transfer process to separate the copper substrate and the graphene, which posts enormous technical challenge for reliable production of large number of sensor arrays. There was a recent attempt on transfer-free batch fabrication of single layer graphene transistors via a low pressure (˜11 Torr) CVD method.70 Yet to the best of our knowledge there has been no report on batch fabrication of graphene sensors, in particular, with suspended device geometry.
In addition, ultrafast detection of short-time chemical exposure is critical for real-time monitoring of active (e.g. toxic) gases, so that an early warning signal can be provided in time for subsequent remedy actions. Graphene suspended from the substrate promises faster response and higher sensitivity by reducing the substrate interference. As previously reported,71-76 suspended graphene demonstrates high carrier mobility exceeding 200,000 cm2V−1s−1, which corresponds to two orders of magnitude higher than that of non-suspended graphene (typically ˜5000 cm2V−1s−1).9 The significant mobility increase by minimizing the detrimental substrate effects has led to important fundamental discovery of the fractional quantum Hall effect in suspended graphene,71,72 but serious technical challenges73-76 remain in the fabrication of such suspended graphene devices and prevent further work in exploring its practical applications.
The present invention overcomes the above-mentioned limitations and allows for the large production of arrays of suspended graphene sensors by combining low cost ambient pressure CVD process with standard nano-fabrication techniques. The resulting suspended graphene nanosensors take advantage of their high carrier mobility to achieve ultrafast molecule detection and to assess the dynamical sensing response on the nano-second time scale. Ultrafast electronic circuits, statistical analysis and first principles simulations are also used to query the dynamical interaction between target molecules and suspended graphene.